Research on High Accurate Measurement on Dual Frequency Signals

To reduce the influence on the measurement accuracy of dual frequency signals such as harmonic and inter-harmonic caused by the non-integer period sampling errors, a new interpolation correction algorithm based on discrete Fourier transform (DFT) is proposed in this paper. The algorithm divides the sampling into four different states. The frequency, amplitude, and phase of the dual frequency signals are calculated by analyzing the relationships between the real part and imaginary part of the spectral peak and sub spectral peak in the discrete spectrum of the signal in each state. There is not error nearly introduced by the algorithm whether the sampling process is in integer period. Therefore, no strict requirement is needed whether the data acquisition system realizes the integer period sampling and no need to use compensation algorithm to improve the accuracy. The simulation results show that the accuracy of the frequency, amplitude, and phase calculated in the algorithm reaches the level of 10−9. The correctness of the algorithm is verified, accuracy meets the calibrating requirements of harmonic and inter-harmonic parameters of power sources, power analyzers and other equipment. At present, the calibration program based on the algorithm has been applied to the calibration of harmonic and inter-harmonic parameters of relevant instruments, and good results have been obtained.